All the quadrilaterals are similar.

All the rectangles are not similar.

Two photographs of the same size of the same person, one at the age of $10 \mathrm{years}$ and the other at the age of $40 \mathrm{years}$ are similar.

In figure, $DE\parallel BC$,  $AD=2 \mathrm{cm}$, $BD=2.5 \mathrm{cm}$, $AE=3.2 \mathrm{cm}$, determine $AC$.

In $△ABC$, $D$ and $E$ are points on the sides $AB$ and $AC$ respectively, such that $DE\parallel BC$. If $AD=5 \mathrm{cm}$, $DB=8 \mathrm{cm}$ and $AC=6.5 \mathrm{cm}$, find $AE$.

In the figure below, if $DE\parallel BC$ and $AD=4x-3$, $AE=8x-7$, $BD=3x-1$ and $CE=5x-3$, find $x$.

In figure, if $AB\parallel CD$, find the value of $x$.